bulb crops

A Primer on Hydroponic Cut

Hydroponic forcing has many foreseeable applications in North America, including both large-scale grower production and small-scale production at the retail level. Find out if this system of production is right for you.

By Bill Miller

ulip are a good example of a flower bulb crop that can be adapted to hydroponic culture. In Holland, approximately 30-35 percent of the cut tulip crop is forced hydroponically, and we have been evaluating this production method at CornellT over the past two seasons. While our experiences have been very positive, there are several important details to understand and act upon before a high-quality crop can be produced.

HYDROPONIC BULB BASICS The basic procedure with hydroponic tulip forcing is to give approxi- mately 75-80 percent of the cold requirement to dry, unplanted bulbs (see Figure 1, below). Depending on the and time of year, this might be 12-14 weeks. Bulbs are then “planted” into the system, and a dilute calcium nitrate solution is added for rooting (about 1.0-1.2 mmhos/cm2). Rooting proceeds at 40° F for 3-4 weeks for early crops or 2-3 weeks for later crops. After the entire cold requirement has been provided, bulbs are moved into the greenhouse for forcing. The are then fed with calcium nitrate, with the goal of maintaining an EC of 1.2-1.5 mmhos/cm2. It is important to realize that the longer the rooting period (above 2-4 weeks), the lower the eventual quality of the flower. This is because longer roots cause more rapid oxygen depletion of the solution and become more susceptible to disease. Also, the longer and more entangled the roots are, the more difficult harvest is (harvesting one stem pulls up many more with entangled roots). Realizing the relatively small root system needed to pro- duce a good-quality is the key to successful hydroponic tulip produc- tion; the small root size is probably much less than is necessary for cut tulips in soil- or peat-based forcing. ➧

Figure 1. Basic scheme for forcing hydroponic cut tulips.

BULBS ARRIVE

CA. 80% PLANT AND Top: Tulip bulbs planted in the Bulbfust “pin-tray.” At this point, bulbs have received about PLACE DRY, OF COLD ADD CALCIUM 40° F 80 percent of their cold requirement (ca. 12-14 weeks). They have been pressed onto the pins, NON-PLANTED RETURN TO NITRATE FORCE and calcium nitrate at an EC of 1.0 has been added. The tray will be placed back into the BULBS IN 12-14 COOLER FOR 2-4 WEEKS WEEKS SOLUTION cooler at 40° F for an additional 2-3 weeks of rooting prior to greenhouse forcing; Bottom: COOLER ROOTING Hydroponic tulip crop upon moving to the greenhouse. At this point, bulbs have received (EC 1.0) their full cooling and will be flowering in ca. 21 days. (All photos courtesy of Bill Miller)

8 GPN August 2002 bulb crops

Compared to traditional “soil” densely packed, unplanted tulips in it is simply due to the prevailing the reduced crop time in the green- culture in “boxes” (where bulbs are their shipping crates); and temperature (ca. 40° F) of the plants house. Plus, in traditional cut flower planted in crates, cooled, then • harvesting is easier and cleaner during the 2- to 4-week rooting peri- forcing in boxes, the mass of the forced), hydroponic forcing has the — there is no wasted soil at the end, od. This is 6-8 degrees warmer than bulbs and soil is substantial, proba- following advantages: greatly reducing material handling is typical during the last few weeks bly taking 1-2 days to warm to pre- • it is 3-5 days faster than soil problems. of cooling, where, normally, temper- vailing greenhouse temperatures. culture; Why do hydroponic plants force atures of 32-33° F might prevail to The disadvantages of hydropon- •much less cooler volume is faster than plants grown in tradition- reduce stem growth in the cooler. ic forcing are: required for chilling bulbs (because al soil culture? It is not due to any These few degrees over a 2- to 4- •When grown at the same most of the cold period is given to inherent superiority of ; week period can easily account for temperature, the ultimate quality of the stem is not quite as good as when the same cultivar is grown in soil (hydro stems tend to be 1-2 inches shorter and 6-8 percent lighter compared to substrate- grown stems); •not all are suited to this system; •very high-quality and disease- free bulbs are required, especially for later plantings (careful attention must be placed on proper bulb stor- age, including temperature, humid- ity and ventilation); •especially for individual trays, a level bench or tray support sys- tem is critical to maintain a level nutrient solution (old, uneven benches won’t cut it); and •the need for exceptional clean- liness. The trays and components are sometimes difficult to wash and sanitize (although, on a large scale, a machine could be used for this).

OPTIONS AND SOLUTIONS The weight and length issues of hydroponic tulips are solvable problems, and ongoing work in

Below are contact numbers for three of the major suppliers of hydroponic forcing systems in The Netherlands. In addition, your bulb supplier may be consulted for additional sources and information.

BulbFust 011-31-227-603582 E-mail: [email protected]

Ons-Belang 011-31-252-343536 E-mail: onsbelang@flowerbulb.nl

Potveer 011-31-229-542324 E-mail: [email protected]

These numbers are provided for conve- nience only and are not intended to be an endorsement. Similarly, omission of information on other manufacturers is not to be taken as criticism of their products.

10 GPN August 2002 bulb crops

The Netherlands indicates that adjustments in As expected, each system has its own plusses tulips. We adapted our irrigation and fertil- rooting period and aeration can compensate and minuses. The Bulbfust “pin tray” has proven ization practices such that new calcium for most of the weight and length reduction. to be popular because it is durable, and the pins, nitrate solution (at an EC of 1.2) was used After considering the biological merits of while causing some injury to the bulbs, are usable during the week, and only clear water was hydroponic forcing, thought must be given to for nearly all sizes of bulbs and provide an infinite applied on weekends. In this way, we were the hydro system itself. A tray designed by the number of spacing and arrangement options. The able to maintain the EC at an acceptable level Bulbfust Company (24 x 16 inches, approxi- plug-like trays are designed for specific bulb sizes, and grow excellent-quality tulips. mately four inches tall, designed to fit inside a and multiple trays are needed if a company forces And even though the solution in hydroponic black plastic bulb crate) is still the major one different sizes of bulbs. In either case, there are trays is only about 1.5-2 inches deep, it is possible used in The Netherlands. It is characterized by a two components to handle: the crate and the for the dissolved oxygen level in the solution to grid of plastic “pins” that the bulb is pressed water tray itself (though this is being solved by drop sufficiently low that root growth is reduced. onto for upright support. The tray has two new, larger-scale systems designed to utilize larg- Research in The Netherlands at the Zwaagdijk drainage holes to maintain the proper solution er ebb-and-flow greenhouse benches). experiment station confirms this and has demon- depth when the tray is level. A number of other Our research at Cornell has indicated that strated the expected advantages of larger nutrient systems are available from manufacturers in static nutrient solution (as is characteristic in reservoirs with solution that flows constantly The Netherlands. These systems are very simi- individual trays) is often difficult to maintain over the roots. In this way, there is a greater lar in appearance to large plug trays and come at optimal EC, aeration and pH levels. The buffering of nutrients, a slower rate of change of in a of sizes to match the size of the bulb volume of solution in each tray is only about pH and EC, and better aeration of the solution. being forced (4-5 inches, etc). 10 liters; this is not a lot of solution for 60-80 Thus, it should be easy to adapt existing ➧

Left: Several cultivars of hydroponic tulips about a week after moving to the greenhouse; Center: Example of the root mass that is typical on hydroponic tulips. Also visible is the grid of “pins” that are characteristic of the Bulbfust hydroponic system; Right: Harvesting of hydroponic tulips in The Netherlands. Notice the lack of soil and very clean roots and stem.

PERENNIALS

Finest Quality Perennials, Ground Covers, Herbs, Wildflowers, Grasses, Ferns, 1800 Varieties, Liners or Finished Products

BLUEBIRD NURSERY, INC. P.O. Box 460 Clarkson, NE 68629 800-356-9164 FAX 402-892-3738

August 2002 GPN 11 bulb crops

Left: A partial assortment of hydroponic forcing inserts (“plug inserts”) for forcing. Note different sizes of holes and bulbs; Center: ‘Monte Carlo’ tulips forced in Bulbfust hydroponic trays without supplemental aeration in 2001; Right: ‘Friso’ tulips grown in the Bulbfust hydroponic system. The bulb on the left is from a tray given supplemental aeration from a small aquarium pump and airstone; the bulb on the right is a control plant, with no supplemental aeration. Aeration given for approximately seven days before this photo was taken. ebb-and-flow benches to hydroponic tulip pro- house operations, where a few trays could be Thanks are expressed to the Dutch Exporters duction. An indication of the plant and root forced weekly to provide very high-quality, local- Association for flowerbulbs and nursery stock, and response to simple aeration of the solution is ly produced products. Because a smaller cooler SePRO, Uniroyal and Valent USA for financial and shown above. Interestingly, the dissolved oxygen volume is needed, capital costs are lower, making material assistance with aspects of the research reported level of our non-aerated treatment was still above it easier to get into cut tulip production. herein. Also thanks to Cornell’s Barbara Stewart and the minimum needed for good growth of hydro- Eliminating the direct cost of the substrate and Jeffrey Wagemaker and Pieter Heemskerk, two Dutch ponic lettuce crops; perhaps this indicates tulips the associated handling costs probably allows for student interns involved with this work. have an especially high dissolved oxygen require- payment of the hydroponic trays in two years ment for growth. Currently, the answer to this (although costs and savings would vary tremen- Bill Miller is professor of flowerbulb and green- question is unknown. dously between companies). Our own experi- house crop physiology in the Department of ence with hydroponic tulips at Cornell has been Horticulture, Cornell University, Ithaca, N.Y. He THE FUTURE very positive, and in most cases, the advantages can be reached by phone at (607) 255-1799 or E- FOR HYDROPONIC TULIPS more than compensate for the negative aspects of mail at [email protected]. It is easy to see hydroponic tulip production this way of forcing. One thing is clear: An ultra- continuing to increase worldwide. In the United fresh cut flower tulip is a beautiful thing and is LearnMore! States and Canada, one can envision its use for rarely seen by most consumers in North large-scale production with all the advantages America. There would seem to be many oppor- For more information noted in this article. It is also easy to see it as an tunities to incorporate hydroponics into the prod- related to this article, go to interesting component for smaller retail green- uct mix of many smaller growers. GPN www.onhort.com/LM.CFM/gp080201

12 GPN August 2002